The inventive subject matter generally relates to implantable medical devices. It particularly relates to implantable devices made of molded plastics and having integrated electronics components, such as RF antennae, conductive elements, functional devices (e.g., resistors, semiconductor chips, RF devices, etc.), and optical guides (e.g., optical fiber).
The inventive subject matter is particularly suited for use with implantable devices for Cardiac Rhythm Management (CRM). Cardiac Rhythm Management Devices (CRMs) generally are small devices that are implanted into a patient's thoracic area. Modern CRM devices typically have a maximum length under 100 mm and a minimum volume of approximately 30 cc.
They send signals to cardiac tissue to stimulate it in response to sensed rhythms. Classes of CRM devices include, among other devices, implantable pacemakers and Implantable Cardiac Difibrillators (ICDs). A pacemaker monitors the electrical impulses in the heart. When needed, it delivers electrical pulses to make the heart beat in a more normal rhythm. A pacemaker may be helpful when the heart beats too slowly or has other abnormal rhythms. An ICD is a device that monitors heart rhythms. If it senses dangerous rhythms, it delivers shocks. Many ICDs record the heart's electrical patterns when there is an abnormal heartbeat. This can help a doctor plan future treatment.
A variety of implantable medical devices have emerged over the decades. Implantable devices are man-made, in contrast to transplantable biological tissues. At least the surfaces of implants are made of biocompatible materials. Such materials include classes of such plastics and/or metals that are known in the medical arts for their biocompatible properties. Implantable devices can be used to replace a missing bodily function, enhance an existing function, or otherwise mediate a function. For example, implants exist for replacement or support of bones and teeth; cardiac rhythm management, drug delivery, cosmetic enhancement, and repair of organs or tissues.
Particular challenges exist in the design and use of implantable devices. For example, many classes of implantable devices need to be small and light weight so that they are minimally invasive. They must also be long lasting to help avoid the need for repeat surgical procedures to service or replace an implanted device.
The challenges inherent in the design of implantable devices having integrated electronics components are particularly onerous. For example, such devices must have proper electrical insulation and grounding to reduce the risk of shorting causing device failure or shock to patients. They must have low power requirements and long battery life for operational longevity. In applications such as cardiac rhythm management, it is critical that devices operate as reliably and safely as possible.
To address at least some of the aforementioned concerns, some implantable devices have been designed using molded plastics. For example, thermoplastics can be injection molded to provide lightweight devices having integrated electronics components. The plastic serves not only to provide a highly configurable shape, but also electrical insulation and hermetic sealing around integrated electronics components. Some applications are seen in US Patent Pub. No. 20090017700.
There are particular challenges to integrating electrical other components into molded plastics. The components must be precisely placed in the body of the device and relative to electrical interconnects or other parts in the body. Shapes must be precisely rendered in the molded form. Injection molding is a favored technique for forming body portions of implantable devices, but there are other forms of molding plastics, such as blow molding, thermoforming, reaction injection molding, compression molding, transfer molding, film insert molding, rotational molding, extrusion molding. Injection molding will generally be used hereafter as a representative example herein.
The very nature of the injection molding process, as well as other molding processes, is at odds with the objectives of precision placement and shaping of components. This is because injection molding involves the injection of pressurized, flowing materials into the cavity of a mold. The force of the flowing material can dislodge components that are positioned in the mold cavity. The flowing material may not completely surround components. Or the materials may not form to dimensions and shapes that meet design specifications and tolerances. These problems can result can result in components being out-of-position, incorrectly formed, or surrounded by air gaps, any of which can cause the implantable device to short circuit or otherwise to function improperly. For example, CRM devices have a “header” portion that includes an antenna for sending or receiving data signals wirelessly to or from a patient's body. An example CRM device 1 implanted into the chest of patient is schematically shown in FIG. 1. A closer schematic view of CRM 1 is shown in FIG. 2. The header 12 also has electrical conductive paths and couplings for connecting to the pulse generator module. The header 12 also has electrical connectors for receiving electrical one or more electrical leads, e.g., leads 14, 16, 18, 20, that connect to heart tissue to sense heart rhythms. In response to sensed rhythms, the header receives signals from the pulse generator 12 and passes them through the leads to stimulate heart tissue into a programmed rhythm. In one suitable design for an antenna 24, as generally indicated, in, for example, FIG. 3, the antenna is a conductive filament disposed along the peripheral sides of the body of the header. Maintaining the position of the antenna in the mold cavity in an injection molding process has proven to be challenging given the length of the filament and its alignment along multiple sides of a small-scale device.
Furthermore, a filament antenna for use in an implantable device typically has a small diameter, a relatively flat cross-sectional profile, or both, that is vulnerable to damage during the relatively high pressure or turbulence of an injection molding process. Thus, a substantial need exists to secure and protect fragile implantable device components, such as antennae, during molding or other fabrication processes.
Given the foregoing exemplary needs and considerations, an ever present need exists for improved molded implantable devices.